Split the filter code into a class.

[c64tapwav] / filter.cpp

diff --git a/filter.cpp b/filter.cpp
new file mode 100644 (file)
index 0000000..d8f9701
--- /dev/null
+++ b/filter.cpp
@@ -0,0 +1,25 @@
+#include <math.h>
+
+#include "filter.h"
+
+void Filter::reset()
+{
+       d0 = d1 = 0.0f;
+}
+
+Filter Filter::lpf(float cutoff_radians)
+{
+       float resonance = 1.0f / sqrt(2.0f);
+       float sn = sin(cutoff_radians), cs = cos(cutoff_radians);
+       float alpha = float(sn / (2 * resonance));
+
+       // coefficients for lowpass filter
+        float a0 = 1 + alpha;
+       float b0 = (1 - cs) * 0.5f;
+       float b1 = 1 - cs;
+       float b2 = b0;
+        float a1 = -2 * cs;
+        float a2 = 1 - alpha;
+
+       return Filter(a0, a1, a2, b0, b1, b2);
+}